The present invention is directed to bicycles and, more particularly, to a bicycle control apparatus that uses an idler member to set the position of a takeup element.
U.S. Pat. No. 5,921,139 discloses an example of a bicycle control apparatus that uses an idler member to set the position of a takeup element. That apparatus comprises a base member with a plurality of first positioning members, an operating member mounted around a handlebar so as to rotate in first and second directions relative to the base member, a takeup element rotatably mounted around the base member for pulling and releasing a transmission control element, and an idler member with a plurality of second positioning members that engage the plurality of first positioning members on the base member. The idler member is coupled to the takeup element so that the idler member rotates integrally with the takeup element, but the idler member is capable of moving axially between engagement and disengagement positions with the base member to set various operating positions of the takeup element. The idler member includes first cam surfaces that cooperate with cam surfaces on the base member to move the idler member between the engagement and disengagement positions when the operating member rotates in the first direction to pull the transmission control element, and the idler member includes second cam surfaces that cooperate with cam surfaces on the operating member to move the idler member between the engagement and disengagement positions when the operating member rotates in the second direction to release the transmission control element.
The rotational positions of the takeup element are determined by the rotational pitch of the plurality of first and second positioning members. Thus, if it is desired to decrease the spacing between successive rotational positions of the takeup element, then it is necessary to decrease the rotational pitch of the plurality of first and second positioning members accordingly. If the positioning members have the form of ratchet teeth, then it becomes more difficult to manufacture the base member and idler member as the rotational pitch decreases. Decreased rotational pitch also usually requires decreased contact area between the first and second positioning members, thus decreasing engagement strength between the idler member and the base member and risking undesirable turning of the takeup element in the wire unwinding direction.
Another design consideration of bicycle control devices is the ability to transfer operating forces between the operating member and the takeup element. Operating forces in conventional designs are transferred between the operating member and the takeup element through the idler member. As a result, large operating forces can result in correspondingly large wear forces applied to the various cam surfaces, thus decreasing service life of the control device.